Various wireless communication techniques are being developed with the development of an information communication technology. Among the techniques, wireless local area network (WLAN) is a technology that can provide a wireless connection to the Internet in a limited service area such as a home or office building using portable terminals, for example, a personal digital assistant (PDA), a laptop computer, and a portable multimedia player (PMP) based on a wireless frequency technology.
A standard for WLAN technology is developed as the Institute of Electrical and Electronics Engineering (IEEE) 802.11 standard. IEEE 802.11a provides a transfer rate of 54 Mbps using 5 GHz unlicensed band. IEEE 802.11b provides a transfer rate of 11 Mbps by using direct sequence spread spectrum (DSSS) in 2.4 GHz band. IEEE 802.11g provides a transfer rate of 54 Mbps by using orthogonal frequency division multiplexing (OFDM) in 2.4 GHz band. IEEE 802.11n provides a transfer rate of 300 Mbps for two spatial streams by using multiple-input multiple-output OFDM (MIMO-OFDM). IEEE 802.11n supports a channel bandwidth of up to 40 MHz and, in this case, provides a transfer rate of 600 Mbps.
With the wide deployment of WLAN and the diversification of applications using WLAN, new WLAN techniques are increasingly needed to support higher throughput than IEEE 802.11n. Very high throughput (VHT) WLAN is one of IEEE 802.11 WLAN techniques, which is proposed to support a data processing rate of 1 Gbps or more. In particular, IEEE 802.11ac is developed as a standard for providing a very high throughput on the 5 GHz band, and IEEE 802.11ad is developed as a standard for providing a very high throughput on the 60 GHz band.
In a system based on the WLAN technology, when a terminal scans an access point through an active scanning scheme, the terminal transmits a probe request frame, and the access point transmits a probe response frame in response to the probe request frame. In an environment in which there are a plurality of terminals and a plurality of access points, each of the terminals transmits its own probe request frame, and each of the access points transmits a probe response frame in response to the probe request frame. That is, a large number of probe request frames and probe responses frames are generated, which occupy many wireless channels. Accordingly, the terminal is required to wait while keeping awake for a long time in order to receive the probe response frame from the access point.